Dynamic vision sensor architecture

Abstract

A dynamic vision sensor (DVS) or change detection sensor reacts to changes in light intensity and in this way monitors how a scene changes. This disclosure covers both single pixel and array architectures. The DVS may contain one pixel or 2-dimensional or 1-dimensional array of pixels. The change of intensities registered by pixels are compared, and pixel addresses where the change is positive or negative are recorded and processed. Analyzing frames based on just three values for pixels, increase, decrease or unchanged, the proposed DVS can process visual information much faster than traditional computer vision systems, which correlate multi-bit color or gray level pixel values between successive frames.

What is claimed is: 
     
       1. A sensor, comprising:
 an array of pixels, each of the pixels including:
 a photosensor that detects incoming light, a photoreceptor signal being a function of an amount of light received by the photosensor; 
 a memory capacitor, wherein first plate of the memory capacitor carries a charge from the photoreceptor signal, and a second plate of the memory capacitor is connected to a comparator node, the voltage of which varies with changes in the photoreceptor signal; 
 one or more comparators that compare voltages of the comparator node to one or more reference voltages to assess changes in the photoreceptor signal with respect to one or more thresholds: and 
 a reset circuit for resetting the memory capacitor in response to a global reset signal and in dependence on a content of a memory structure that stores an output of the one or more comparators. 
 
 
     
     
       2. A sensor as claimed in  claim 1 , further comprising a photoreceptor circuit between the photosensor and the memory capacitor. 
     
     
       3. A sensor as claimed in  claim 2 , wherein the photoreceptor circuit provides a logarithmic response to a current from the photosensor. 
     
     
       4. A sensor as claimed in  claim 1 , wherein the second plate of the capacitor is directly connected to the comparator. 
     
     
       5. A sensor as described in  claim 1 , further comprising a switch for connecting the photosensor to the memory capacitor. 
     
     
       6. A sensor as described in  claim 1 , wherein the photosensor comprises a photo diode, a photo transistor, or a photoactive area. 
     
     
       7. A pixel assembly comprising:
 one or more pixels, each of the one or more pixels comprising: a photodiode which can convert light which is incident on the photodiode into a current, wherein the amplitude of said current is proportional to the intensity of the light; a photoreceptor which is connected to the photodiode so that the photoreceptor can receive said current from the photodiode, and wherein the photoreceptor is configured such that it can convert said current which it receives from the photodiode into a voltage and to output that voltage as an output of the photoreceptor; and a capacitor; 
 at least one comparator having a first and second input, wherein the first input can be set to a threshold voltage and wherein the capacitor is electronically connected to the second input so that the capacitor is between the output of the photoreceptor and the second input of the comparator; 
 a memory which is electronically connected to an output of comparator such that a value which is output by the comparator can be allocated and stored in the memory; 
 a reset circuit assembly which is configured such that it is selectively operable to set the voltage at the second input of the comparator to a predefined reference voltage; and 
 a controller which is configured to apply a threshold voltage to the first input of the comparator, and after the threshold voltage has been applied to the first input of the comparator initiate the memory to store the value which is output by the comparator, and after the memory has stored said value output by the comparator initiate the reset circuit to set the voltage at the second input of the comparator to a predefined reference voltage depending on the value which was stored in memory. 
 
     
     
       8. A pixel assembly according to  claim 7 , wherein the comparator is configured to output a first value if the difference between the threshold voltage applied to the first input of the comparator and the voltage at said second input of the comparator is larger than a predefined amount; and wherein the controller is configured to initiate the reset circuit of the pixel to set the voltage at the second input of the comparator to a predefined reference voltage if the value which was stored in memory is a first value. 
     
     
       9. A pixel assembly according to  claim 8 , wherein the comparator is configured to output a second value if the difference between the threshold voltage applied to the first input of the comparator and the voltage at said second input of the comparator is smaller than a predefined amount; and wherein the controller is configured to initiate the reset circuit of the pixel to set the voltage at the second input of the comparator to a predefined reference voltage if the value which was stored in memory is a second value. 
     
     
       10. A pixel assembly according to  claim 7 , wherein each of the one or more pixels comprise a single capacitor only. 
     
     
       11. A pixel assembly according to  claim 7 , wherein said memory is integral to the pixel, and wherein the assembly comprises a plurality of said pixels which define a pixel array, and wherein the respective memory of each of the one or more pixels in the pixel array have an address which is unique to the addresses of all of the other memories of the other pixels in said array. 
     
     
       12. A pixel assembly according to  claim 11 , wherein the pixel assembly further comprises a read-out circuit, and wherein the read-out circuit is configured such that it can selectively read the content of the memory of each of the pixels in the array and to output to a processor the addresses of those memories which have a predefined content. 
     
     
       13. A pixel assembly according to  claim 11 , wherein the controller is configured to apply a threshold voltage to the first input of the comparator of each pixel in the array, and after the threshold voltage has been applied to the first input of the comparators to initiate the respective memories of those respective pixels to store the respective values output from the respective comparators; and
 wherein the pixel assembly further comprises a read out circuit which is configured to read the memories after they have stored the values which output from the respective comparators. 
 
     
     
       14. A pixel assembly according to  claim 13 , wherein the controller is configured to apply a first threshold voltage to the first input of the comparator of each pixel in the array, and after the first threshold voltage has been applied to the first input of the comparators to initiate the respective memories of those respective pixels to store the respective values output from the respective comparators; and
 wherein the pixel assembly further comprises a read out circuit which is configured to read the memories after they have stored the values which output from the respective comparators; and 
 wherein the controller is further configured to then apply a second threshold voltage to the first input of the comparator of each pixel in the array, and after the second threshold voltage has been applied to the first input of the comparators to initiate the respective memories of those respective pixels to store the respective values output from the respective comparators; and 
 wherein the pixel assembly further comprises a read out circuit which is configured to read the memories after they have stored the values which are output from the respective comparators. 
 
     
     
       15. A pixel assembly according to  claim 14 , wherein the read-out circuit is further configured to output address(es) of the memories which have a value which corresponds to a predefined value.